This invention relates to a method for the polymerization and copolymerization of olefinic monomers. More particularly this invention relates to an improved method for the polymerization of isobutylene and its copolymerization with butadiene.
High molecular weight polyisobutylene and copolymers of isobutylene with isoprene are currently being produced at low temperatures, such as -80.degree. to -100.degree. C. The limiting factor in the low temperature method for producing butyl rubber is the choice of an appropriate diene comonomer. The industrial methods now in use are all based on the copolymerization of isobutylene with isoprene. This is the case despite the fact that butadiene is a cheaper and more readily available diene monomer than isoprene. The isoprene is used rather than the butadiene because of its more acceptable copolymerization reactivity ratio with respect to the isobutylene. The reactivity ratio of isoprene to isobutylene is virtually independent of temperature, while that of butadiene decreases with decreasing temperature. Butyl rubber having the required amount of double bonds could not heretofore be prepared by the copolymerization of isobutylene with butadiene at temperatures of about -100.degree. C. At higher temperatures, products having low molecular weights only were obtained, such products being entirely unsuitable for use in the production of vulcanized articles.
There is disclosed in Czechoslovak Pat. Nos. PV 2712-70 and PV 2792-70, combined in U.S. patent application Ser. No. 133,545 abandoned and refiled as Ser. No. 184,637 filed Sept. 28, 1971, that the polymerization of monomers having olefinic double bonds in their molecules can be carried out using a cationic system and accelerated by light, in the presence of halides of tetravalent titanium, vanadium and zirconium.
In accordance with the invention, it has now been found that the polymerization carried out in the presence of the aforesaid halides and under the influence of light (visible ultraviolet or infra red) takes place more readily when it is conducted in the presence of certain activators, for instance, metal oxides, hydroxides and alkoxides. The activators may be present in the polymerization medium in the form of their solutions or as fine suspensions. In the presence of these activators, the polymerization reaction proceeds not only more readily but also more rapidly than heretofore possible.